Shibaura ST318, Workshop Manual

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2) Structure and fun c tion of each part
1. Spool and sleeve
➀
The spool and sleeve are rotary valves to change the direction or combination of the oil passage. Three combinations
are possible (neutral, right steering and left steering) by handle operation.
➁ The spool and sleeve are mechanically linked to the B and C section as shown in the figure below.
A: The spool and sleeve are linked by leaf spring.
When the handle is released or not moved in either side, the spool and sleeve are kept at the neutral position by
the force of the leaf spring.
B: Spool and sleeve are linked by the pin.
The sleeve and drive are linked with the pin positively leaving no play.
The spool hole is oval to allow the spool to move laterally with respect to the pin (see the figure below), for the
purpose of composing oil passage for the right and left turn by deviating the spool laterally to the sleeve.
2. Drive
Movement of the gear pump (Gerotor) is transmitted to the sleeve. When the engine or oil pump fails, power of the
operator is transmitted to the internal gear of the gear pump through the spool and pin.
3. Gear pump (Gerotor)
When engine or oil pump is subjected to trouble, the gear pump is driven by the operator and serves as an emergency
auxiliary pump.
4. Check valve
When oil is fed under pressure from the oil pump, the check valve prevents flow of oil from IN to OUT and when the
engine or oil pump fails, the valve is opened to allow the oil to be sucked from the oil tank to the IN side.
5. Relief valve
When the steering wheel is turned fully clockwise or counterclockwise, the relief valve protects the pump and hydraulic
circuit.
T610